Stopper Rod

ABSTRACT

A stopper rod for controlling the flow of molten steel from a tundish has a metal carrier element partly received in an internal passageway of the stopper rod, the carrier element compressing sealing means between a frustoconical undersurface of a laterally enlarged portion thereof and a complementary seating surface of the stopper rod passageway, there being an insert threadedly engaged with one of the carrier element and stopper rod body at a position above a laterally enlarged portion of the carrier element, with further sealing means disposed between said insert and the carrier element. Preferably the insert is a nut screwed down onto a washer which compresses the further sealing means.

This invention relates to a stopper rod for controlling the flow ofmolten metal, for example from a vessel, such as a tundish, to a mould,and more preferably, to a stopper rod for supplying an inert gas to themelt in the vessel.

Such a stopper rod is well known, it being moved in the direction of itslongitudinal axis by a lifting device external to the vessel in whichthe stopper rod is disposed, so that an outlet opening in the base ofthe vessel, into which the stopper rod fits at its lowest position,shutting it off completely, is opened either more or less. The flow ofmetal through the opening is thus controllable.

However extreme conditions prevailing in the processing of steel placesevere demands on the materials and the engineering of the stopper rod,which has to withstand the effects of molten metal over the course ofmany hours. It must also be able to withstand the wide variations intemperature acting on the stopper rod during a pouring process. Moreoverwhere the stopper rod serves to introduce an inert gas to the metalmelt, it is important that no air reaches the interior of the stopperrod and thus the metal melt through the connection between the stopperrod body and the part of the lifting device which extends into saidbody, since this would lead to increased oxidation and thus adeterioration in steel quality. This connection is particularlyproblematical owing to the high thermal and mechanical loads acting onthe connection. The difference in respective thermal expansioncoefficients between different materials involved in the connection, inparticular, needs to be compensated or allowed for.

An object of the invention is to provide a stopper rod in an improvedform.

According to the invention there is provided a stopper rod comprising arefractory material stopper rod body having an internal passagewayextending from a first end of the body towards a second end thereof, ametal carrier element having one of its ends received in saidpassageway, the carrier element having a laterally enlarged portionreceived in a laterally enlarged portion of the passageway, whichpassageway portion defines a seating surface, and sealing means betweensaid seating surface and an underside of the laterally enlarged portionof the carrier element, wherein an insert is threadedly engaged with oneof the carrier element and the stopper rod body at a position above saidlaterally enlarged portion of the carrier element, with further sealingmeans being disposed between said insert and the carrier element.

Preferably the carrier element, which serves, in use, to connect thestopper rod to a lifting device, has a gas supply passage extendingtherethrough.

Desirably the sealing means is a graphoil seal. In one embodiment theinsert is threadedly engaged with the carrier element. In thatembodiment the further sealing means is a packing gland seal. In anotherembodiment the insert is threadedly engaged with the stopper rod body.In that embodiment the further sealing means is a graphoil seal, whichis preferably thicker than the graphoil seal forming said sealing means.In a still further embodiment the insert is threadedly engaged with aceramic insert which is preferably pressed into the stopper rod to formpart thereof.

Conveniently the sealing means is disposed between complementaryfrustoconical surfaces respectively of the enlarged portion of thecarrier element and said seating surface. Until the stopper rod heatsup, the sealing means is compressed between the carrier element and thestopper rod body and provides a gas-tight seal therebetween. As thestopper rod heats up, gas tightness is maintained by the further sealingmeans, even if the seal provided by the sealing means starts to leak dueto the expansion of the metal carrier element.

Advantageously in said one embodiment the insert is engaged with acomplementary thread on the carrier element. The insert is screwed downtightly on the further sealing means to effect radial sealing to theinner annular wall of the passageway of the stopper rod body. Onexpansion of the metal carrier element, the whole assembly simply slidesup fractionally, but the force on the further sealing means, and hencethe gas-tightness, is maintained.

In said another embodiment the insert is a collar, which can be metallicor ceramic, threadedly engaged with a corresponding thread at an upperinner surface of the internal passageway in the stopper rod body. Thethread can be pressed in the stopper rod body passageway, or provided bya pressed-in ceramic insert forming part of the stopper rod body.Initially the collar is tightened to compress the further sealing means.On expansion of the metal carrier element, the further sealing meanswill be subject to additional compressive forces between the expandingcarrier element and the restrained collar to provide an effectivegas-tight seal.

In a preferred embodiment according to the present invention the insertis in the form of a nut screw-threadedly engaged on the carrier element,which nut, when tightened, effects axial compression of said furthersealing means, resulting in sealing between the stopper rod body and thecarrier element.

The nut preferably effects axial compression of said further sealingmeans through the intermediary of a washer. Desirably the washer islocated around the carrier element at one end of the stopper rod body.Conveniently the washer is larger than the further sealing means, andparticularly of larger diameter than the diameter of the upper end ofthe internal passageway in the stopper rod body, in which upper end thefurther sealing means is received. The further sealing means ispreferably two graphoil seals which stand proud of said upper end of thestopper rod body when the nut is untightened, and are axially compressedinto said upper end of the passageway when the nut is tightened onto thewasher to cause the washer axially to compress the graphoil seals.

The invention will now be described, by way of an example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic side view of the interior of the upper end of aprior art stopper rod,

FIG. 2 is a view like FIG. 1, for a stopper rod of the invention, and

FIG. 3 is a similar view to FIG. 2, for a stopper rod according to afurther embodiment of the invention,

FIG. 4 is a view like FIG. 3 of a stopper rod according to a stillfurther embodiment of the invention, and

FIG. 5 is a split schematic cross-sectional view of the upper end of astopper rod of the invention, the left half showing sealing meansuncompressed, and the right half showing the sealing means compressed.

FIG. 1 schematically shows the upper end of a prior art stopper rod 10having a conventional stopper rod body 11 of refractory/ceramicmaterial. Extending centrally, axially within the stopper rod body 11from the upper end thereof is a circular cross-section longitudinal bore12. A short way down from the upper open end of the bore, it is steppedinwardly to form a frustoconical shoulder defining a seating surface 13.Extending downwards from this surface 13 is a constant diameter circularcross-section part, which leads to a radially enlarged portion of thebore in which is secured a ceramic insert 14, the insert being securedto the stopper rod body 11. Below this insert 14, the remainder of thebore 12 has the same diameter as the part between the surface 13 and theinsert 14. Accordingly the uppermost part of the bore 12 down to andincluding the surface 13 is a laterally (radially) enlarged portion ofthe bore 12. Instead of being ceramic, the insert could be of metal orof cermet material.

Extending into this upper part of the bore 12 is, as shown in FIG. 1, ametallic carrier rod 15, which at its upper end outside of the bore 12is fixed in any convenient manner to a lifting device for raising andlowering the stopper rod, in use, in a vessel such as a tundish, in thenormal manner. The carrier rod 15 is of circular cross-section, but isprovided with a laterally (radially) enlarged portion in the form of anannular collar 16, the external shape of which substantially matches thelower end of the bore 12 above the surface 13 together with the surface13 itself. In other words the upper part of the collar is cylindrical,as at 17, whilst the lower part is in the form of a frustoconicalsurface 18 matching the frustoconical seating surface 13. Below thecollar 16, the carrier rod 15 is of its normal circular diameter, butthis is provided with an external thread at the position of the insert14, so that the engagement of the rod 15 with the insert 14 enables alifting of the carrier rod 15 to be transmitted to the stopper rod body11 so as to lift or lower the stopper rod 10 in use in the normalmanner. As shown in FIG. 1, there is disposed between the correspondingfrustoconical surfaces 13 and 19 a graphoil seal 19. Although not shown,it would normally be the case that there is a gas flow passagewaythrough the centre of the carrier rod 15 for transmitting inert gas, inthe normal way, into the lower part of the bore 12 in the stopper rodbody 11, this inert gas generally being supplied through an opening inthe lower nose part of the stopper rod into the molten metal in thevessel in which the stopper rod is received.

A problem with the prior art system shown in FIG. 1 is that when thestopper rod becomes heated, in use, the thermal expansion of the carrierrod 15 leads to reduced pressure being applied to the graphoil seal 19,resulting in leakage.

The embodiment of the present invention shown in FIG. 2 is designed tosolve that problem. As can be seen from the drawing, all the features ofthe stopper rod shown in FIG. 1 are present in FIG. 2 and haveaccordingly been numbered identically, but with the suffix a. Toovercome the sealing problem identified with the FIG. 1 arrangement, itcan be seen that in FIG. 2 an insert in the form of a nut 20 isthreadedly engaged on the carrier rod 15 a at a position somewhat abovethe upwardly facing surface of the cylindrical part 17 of the collar 16so that, as shown, the upper face of the nut 20 is substantially flushwith the upper face of the stopper rod body 11. Between the lower end ofthe nut 20 and the upper surface of the cylindrical part 17 of thecollar 16 is sealing means in the form, for example, of a packing glandseal 21. Generally this seal 21 would be compressed by the screwing downof the nut 20, even when the stopper rod is not heated, so that theresome radial sealing as shown by the arrows at the seal 21 in FIG. 2.Accordingly instead of the bore 12 being open at above the collar 16 asin FIG. 1, this part of the bore 12 now receives the nut 20 and seal 21as shown.

Accordingly with the arrangement shown in FIG. 2 radial sealing by meansof the seal 21 is maintained even when there is thermal expansion of thecarrier rod 15 a (and nut 20), given that the nut is connected to thecarrier rod 15 a. Although, as the metalwork expands, the whole assemblysimply slides up fractionally, the force on the seal 21, and hence thegas-tightness, is maintained, even though there may be leakage at thegraphoil seal 19 a. Instead of being metallic, the nut 20 could beceramic, of cermet or potentially of any other heat resisting, shapemaintaining material, and both the seal 19 a and the seal 21 could be ofmaterials different from those described. Although not shown with eitherFIG. 1 or FIG. 2, it will be understood that, as is well known withstopper rods, some means of restraint at the top of the stopper rod bodycould be provided around the part of the carrier rod which extends outof this end of the stopper rod body. Such means will be described inrelation to FIG. 3, and it will be understood that these could beapplied equally to the arrangement of FIG. 2.

The embodiment of the invention shown in FIG. 3 is similar in manyrespects to that shown in FIG. 2 and again like components will besimilarly numbered, but with the prefix b. Accordingly it can be seenthat the stopper rod shown in FIG. 3 comprises a refractory/ceramicstopper rod body 11 b with a longitudinal bore 12 b extendingtherethrough from its open upper end. This upper laterally (radially)enlarged part of the bore 12 b is formed with a seating surface 13 b offrustoconical form, and spaced below this surface 13 b there is pressedinto the material of the body 11 a fixing insert 14 b with which anexternally threaded end of the metallic carrier rod 15 b is engaged sothat a lifting or lowering of the carrier rod will result in acorresponding lifting or lowering of the stopper rod in its vessel.

The carrier rod 15 b, which is preferably metallic, has a central gaspassage 22 extending therethrough. It is provided externally with acollar 16 b made up of an upper cylindrical part 17 b and a lower partwhich has a frustoconical undersurface 18 b. As with the FIG. 2arrangement, a seal 19 b, preferably a graphoil seal, is trapped betweenthe frustoconical surface 18 b and the seating surface 13 b to provide agas tight seal when the stopper rod is unheated.

A screw thread 23 is provided, for example by pressing, into the innersurface of the upper part of the bore 12 b and an insert in the form ofan annular collar 24 or equivalent is screw-threadedly engaged with thethread 23, there being, as shown, radial clearance between the innercylindrical surface of the collar and the outer cylindrical surface ofthe carrier rod 15 b. This is in contrast to the FIG. 2 arrangement,where this radial clearance can be provided between the external surfaceof the nut 20 and the inner cylindrical surface of the bore in which thenut is received.

It can be seen from FIG. 3 that trapped between the lower surface of thecollar 24 and the upwardly facing top surface of the collar 16 b is athick graphoil seal 25, which radially seals against the inner surfaceof the bore 12 b below the upper internally threaded part thereof.

The collar 24 is screwed down onto the seal 25 which is compressedthereby. Accordingly when the stopper rod is unheated, there is sealingboth by way of the seal 19 b and also by way of the seal 25, both ofwhich seals are under compression. However as the stopper rod is heated,and the carrier rod 15 b expands, the seal 19 b is likely to start toleak in the normal manner as the compression thereof decreases due tothe expansion of the carrier rod 15 b. However the upper seal 19 b,which is restrained by the fixed screwed-in collar 24, will be subjectto additional compressive forces between the expanding carrier rod 15 band the retained collar 24 to provide an effective gas-tight seal. FIG.3 shows a conventional washer 26 on the carrier rod 15 b at the top ofthe stopper rod body 11 b, this washer being field down onto the top ofthe stopper rod body by a nut 27 which is screw threaded onto thecarrier rod 15 b, the washer and nut providing a conventional lock atthe top of the stopper rod body.

It is believed that the arrangement shown in FIG. 3 is advantageous inthat the force on the seal 25 will increase as the metalwork expands. Insome instances it may be necessary for the stopper to be bandedexternally to overcome any problems as a result of the need to threadthe refractory material of the stopper rod body.

Any such problems with threading the refractory material of the stopperrod body are overcome by the FIG. 4 embodiment, where the thread 23 afor the engagement of the collar 24 is provided by a ceramic insert 28co-pressed into the stopper rod body to form part thereof. As shown, theupper part of the seal 25 is received in a lower non-threaded part ofthe insert 28.

Accordingly with each of the embodiments shown in FIGS. 2, 3 and 4 thethermal expansion/sealing problem identified with the prior art stopperrods is overcome in a simple, yet effective manner.

The stopper rod of the invention shown in FIG. 5 is similar in severalrespects to that shown in FIG. 3, having a stopper rod body 11 c ofrefractory/ceramic material with a central, longitudinally extendingcircular cross-section bore 12 c, which is open at the end of thestopper rod which is uppermost in use. This upper laterally (radially)enlarged part of the bore 12 c is formed with a seating surface 13 c offrustoconical form, and spaced below this surface there is pressed intothe material of the body 11 c a (ceramic) fixing insert 14 c with whichan externally threaded end of the preferably metallic carrier element inthe form of a rod 15 c is engaged, so that a lifting or lowering of thecarrier rod will result in a corresponding lifting or lowering of thestopper rod in its vessel.

The carrier rod 15 c has a central gas passageway through it. It has anexternal collar 16 c made up of an upper cylindrical part 17 c and alower part with a frustoconical undersurface 18 c. A seal 19 c,preferably a graphoil seal, is trapped between the surface 18 c and theseating surface 13 c to provide a gas tight seal when the stopper rod isunheated.

Above the collar 16 c, at least part of the carrier element outside ofthe bore 12 c is externally screw-threaded as shown at 28. Aconventional washer 26 c is received on the carrier element, as with theFIG. 3 embodiment, with a conventional insert in the form of a nut 27 c,also as in the FIG. 3 embodiment, being engaged on the screw thread 28,to force the washer downwardly when the nut is tightened. The washer isof a diameter much greater than that of the bore 12 c at the top of thestopper rod body.

Disposed around the carrier rod 15 c and supported by the upwardlyfacing top annular surface of the collar 16 c is further sealing meansin the form of two graphoil seals 25 a and 25 b. When these seals areaxially uncompressed the upper seal stands proud of the upper end of thestopper rod body. This is shown at the left hand side of the drawing.Here the nut 27 c is in a loosened state, such that there is no forceexerted by the nut on the washer 26 c. The weight of the washer alongacts on the seals, but does not axially compress them. Thus as they arenot radially compressed there is no effective seal produced by thembetween the carrier rod and the stopper rod body.

However if the nut 21 c is now tightened, as shown at the right handside of the drawing, it moves down the screw-thread 28 of the carrierrod and forces the washer 26 c axially downwardly axially to compressthe seals 25 a, 25 b to the position shown at the right hand side, withthe washer engaging the top of the stopper rod body. The axialcompression of the seals causes them to expand radially and form agas-tight seal (as shown) between the carrier rod and the stopper rodbody.

It will be understood that in an alternative embodiment, the washercould be sized to be received in the upper end of bore 12 c and thus atleast partly received therein when it axially compresses the seals 25 a,25 b. In a still further embodiment, the insert screw-threaded on thecarrier rod, such as nut 27 c, could also at least partly be received inthe bore 12 c pressing down on the washer. In other words thearrangement could be similar to that of FIG. 2, but with the addition ofthe washer between the insert and the further sealing means. The furthersealing means could, in any embodiment, be a single seal or any suitablenumber of seals. With these alternative embodiments it is not of coursenecessary for the seal or one or more of the seals to stand proud whenuncompressed.

1-25. (canceled)
 26. A stopper rod comprising a refractory materialstopper rod body having an internal passageway extending from a firstend of the body towards a second end thereof, a metal carrier elementhaving one of its ends received in said passageway, the carrier elementhaving a laterally enlarged portion received in a laterally enlargedportion of the passageway, which passageway portion defines a seatingsurface, and sealing means between said seating surface and an undersideof the laterally enlarged portion of the carrier element, wherein aninsert is threadedly engaged with one of the carrier element and thestopper rod body at a position above said laterally enlarged portion ofthe carrier element, with further sealing means being disposed betweensaid insert and the carrier element.
 27. A stopper rod as claimed inclaim 26, wherein the insert is in the form of a nut screw-threadedlyengaged on the carrier element, which nut, when tightened, effects axialcompression of said further sealing means, resulting in sealing betweenthe stopper rod body and the carrier element.
 28. A stopper rod asclaimed in claim 27, wherein the nut effects axial compression of saidfurther sealing means through the intermediary of a washer.
 29. Astopper rod as claimed in claim 28, wherein the washer is located aroundthe carrier element at one end of the stopper rod body.
 30. A stopperrod as claimed in claim 28, wherein the washer is larger than thefurther sealing means.
 31. A stopper rod as claimed in claim 30, whereinthe washer is of larger diameter than the diameter of the upper end ofthe internal passageway in the stopper rod body, in which upper end thefurther sealing means is received.
 32. A stopper rod as claimed in claim28, wherein the further sealing means is two graphoil seals which standproud of said upper end of the stopper rod body when the nut isuntightened, and are axially compressed into said upper end of thepassageway when the nut is tightened onto the washer to cause the washeraxially to compress the graphoil seals.
 33. A stopper rod as claimed inclaim 26, wherein the further sealing means comprise three separategraphoil seals.
 34. A stopper rod as claimed in claim 26, wherein thecarrier element, which serves, in use, to connect the stopper rod to alifting device, has a gas supply extending therethrough.
 35. A stopperrod as claimed in claim 26, wherein the sealing means is a graphoilseal.
 36. A stopper rod as claimed in claim 26, wherein the insert isthreadedly engaged with the carrier element.
 37. A stopper rod asclaimed in claim 36, wherein the further sealing means is a packinggland seal.
 38. A stopper rod as claimed in claim 26, wherein the insertis threadedly engaged with the stopper rod body.
 39. A stopper rod asclaimed in claim 38, wherein the further sealing means is a graphoilseal.
 40. A stopper rod as claimed in claim 39, wherein the graphoilseal is thicker than the seal forming the sealing means.
 41. A stopperrod as claimed in claim 26, wherein the insert is threadedly engagedwith a ceramic insert.
 42. A stopper rod as claimed in claim 41, whereinthe ceramic insert is pressed into the stopper rod to form part thereof.43. A stopper rod as claimed in claim 26, wherein the sealing means isdisposed between complementary frustoconical surfaces respectively ofthe enlarged portion of the carrier element and said seating surface.44. A stopper rod as claimed in claim 43, wherein until the stopper rodheats up, the sealing means is compressed between the carrier elementand the stopper rod body and provides a gas-tight seal therebetween. 45.A stopper rod as claimed in claim 36, wherein the insert is engaged witha complementary thread on the carrier element.
 46. A stopper rod asclaimed in claim 45, wherein the insert is screwed down tightly on thefurther sealing means to effect radial sealing to the inner annular wallof the passageway of the stopper rod body.
 47. A stopper rod as claimedin claim 38, wherein the insert is a collar.
 48. A stopper rod asclaimed in claim 47, wherein the collar is metallic or ceramic,threadedly engaged with a corresponding thread at an upper inner surfaceof the internal passageway in the stopper rod body.
 49. A stopper rod asclaimed in claim 48, wherein the thread is pressed in the stopper rodbody passageway.
 50. A stopper rod as claimed in claim 49, wherein thethread is provided by a pressed-in insert forming part of the stopperrod body.